The following description of the background of the invention is provided simply as an aid in understanding the invention and is not admitted to describe or constitute prior art to the invention.
Chemiluminescence immunoassays which employ acridinium labels have advantages of high throughput and high analytical sensitivity for low-level analytes of clinical significance. Usually it is desirable to use labeled antibodies with a large number of chemiluminescent tags, which produce high luminescence counts, which, in turn, allows one to achieve lower detection limits. This holds true provided that non-specific binding can be minimized.
During conjugation of antibodies with presently available labeling reagents at relatively high reagent-to-protein ratios, low recoveries of the labeled proteins are often obtained. In most of these labeling reactions, protein precipitation and/or formation of protein aggregates have been observed. Presumably, the precipitates and aggregates are the result of protein molecules with higher degree of labeling than the immunologically active conjugates, which remain in solution. The tendency towards precipitation and aggregation can be attributed to the hydrophobic nature of the four-ring aromatic acridinium ester label.
Accordingly, there is a need in the art for acridinium labeling reagents which have a reduced propensity to cause protein precipitation and/or promote formation of protein aggregates.